resource - projecting curve onto heightfield with control

 Projecting a Road Curve onto a Heightfield - procegen - Procedural Content Generation (konstantinmagnus.de)

some of the newer tools in Houdini might do this, but it's quite nice to see how to do it manually.

point wrangle the curve, with heightfield in input 1..

float lift = chf('lift'); f@height = volumesample(1, 'height', v@P) + lift;

then plug that into a volume wrangle (input 1), heightfield in input 0 

float width_min = chf('min_width'); float width_max = chf('max_width'); float ease = chf('roll_off'); int prim; vector uvw; float dist_crv = xyzdist(1, v@P, prim, uvw); float height_crv = primuv(1, 'height', prim, uvw); float mask = 1.0 - smooth(width_min, width_max, dist_crv, ease); f@height = lerp(f@height, height_crv, mask); f@mask = mask;

You can control the height with the "lift" slider made in the point wrangle, and the width/falloff in the sliders made in the volume wrangle.